This application claims priority to German patent application DE 20 2007 013 281.6 filed 21 Sep. 2007 and which is hereby incorporated by reference herein. The invention relates to a liquid filter composed of a metal housing configured to receive a filter medium.
Examples of such liquid filters are fuel filters for diesel engines. These are routinely operated as full-flow filters and are composed of a cylindrical housing, for example made of metal, in which there is received a filter medium through which fuel to be treated flows and which exerts a retaining function on entrained solid particles, which can be considered as impurities, and of a cover releasably connected to one end side of this housing. The housing can additionally be configured with a view to trapping entrained water. The cover is provided in each case with bores which are intended for the connection of pipe elements serving respectively for delivering and discharging fuel.
Fuel filters form a wear part on which increasing demands are placed in view of the fuel purity demanded for modern injection systems, and therefore there is particular interest in a filter which can be produced economically. It is known to produce the housing of such a filter from aluminium or steel using a deep-drawing process and to produce the cover from the same material using a pressing process, in particular extrusion, wherein the possibilities available in principle for producing a connection with the said pipe elements comprise screwing or else soldering, brazing or welding. Such a fuel filter is also known from U.S. Pat. No. 6,306,92 B1, for example.
The production of the cover by extrusion is characterized by a comparatively expensive die and finishing processes and cannot be regarded as ideal for this very reason. The use of soldering or welding techniques to attach the pipe elements can also be considered as expensive, specifically not least because of the associated outlay on energy, apparatus and manual labour. A comparable situation also applies to the said threaded connections in which a considerable production outlay likewise arises as a result.
Against the economic background where liquid filters, in particular fuel filters, can be regarded as mass-produced products and have to be made available in large quantities, the design forms produced using the above-described techniques appear inappropriate with regard to the resultant cost requirement.
FR 2 864 910 A1 discloses a fuel filter which is composed of a housing receiving a filter body and of a cover which can be placed in a sealing manner on a central connecting stub of the housing, in which cover delivery lines, return lines and outlet lines for fuel are integrated. The cover made of plastic is connected via a latching engagement to the housing, likewise made of plastic.
A further variant of a fuel filter is disclosed in EP 0 537 520 A1 and is composed of a cover in whose central opening a connecting plug formed from soft rubber is inserted in a sealing manner, this plug in turn serving to receive pipelines intended for the inflow and the outflow of fuel.